This invention is concerned with progressive scan displays that are developed from the two fields of an interlaced scan system. The resolution of interlaced scan displays is limited due to the fact that each field, which consists of one half the total number of lines in a frame, is separately displayed, with the lines of the alternate field being black. (The lines of the next field are then displayed with the lines corresponding to the alternate field being black). In the NTSC system, interlaced fields are displayed every 1/60th second and a complete frame is displayed every 1/30th of a second. In a progressive scan display arrangement, in the simplest case, the number of scan lines visible at a given instant is twice that which is visible in a corresponding interlaced system. The conversion may be accomplished by scanning the interlaced video at twice the horizontal rate to double the number of scan lines of video information and displaying all of the real video information or pixels in both fields and interpolating the pixels in each line (that would normally be black) between the lines of real pixels in each field.
Many systems for interpolating video pixel information for progressive scan systems are known. The simplest system averages the pixel values in the lines immediately above and immediately below the interpolated or desired pixel to form an average or intrafield pixel value. While filling in the black between alternate lines, this method neither provides increased resolution nor eliminates the flicker, associated with small details, which appears primarily in one field of the scanned image. A slightly more complex method stores one field and uses it to fill the spaces in the following field. This approach is satisfactory except in the presence of motion in the video. A moving object will be in a different location in the two original fields (and presented properly in these two locations at two different times in an interlaced display), but the interpolated frame, made up of two fields, will present the object in one location on even lines and in the other location on odd lines, thus producing a double image of the object. Most interpolation systems try to compensate for the presence of motion by sampling pixel values in an area around the desired pixel and extending the sampling to fields on either side of the desired interpolated pixel. Difficulties arise in interpolating pixels in interlaced video systems because the sampling is not among pixels that are in the same spatial location in the immediately prior and immediately subsequent fields of the interpolated pixel. Also, in the event of a scene change, i.e. an event involving a substantial amount of video change, the prior art systems tend to break down.